Chromium-plated box wall for molding boxes



Jan. 26, 1965 R. WEHINGER CHROMIUM-PLATED BOX WALL FOR MOLDING BOXES Filed Jan. 21, 1965 5 m 4 A ..r

United States Patent 3,166,796 CHROMIUM-PLATED BOX WALL FDR MOLDlNG BOXES Robert Wehinger, Hard, Austria (Achergasse, Industriegelaude 0st, Vienna-Neustadt, Austria) Filed Jan. 21, 1963, Ser. No. 252,986 Claims priority, application Austria, Jan. 27, 1962,

A 693/62 4 Claims. (Cl. 18-47) The present invention relates to a chromium-plated box wall for molding boxes in plaster molding machines for the production of plaster plates of high accuracy with respect to size and of high surface finish which are cast standing on edge in the molding machine and are discharged from it under pressure.

Such machines consist essentially of a series of directly contiguous molding boxes standing on edge with two opposite narrow open sides. One narrow side serves to accommodate a hydraulically operated ram which can be displaced along the entire height of the box, and the other narrow side serves as an aperture for introducing a paste of plaster. When the paste which has been introduced into the box has set, the plate which is still moist is discharged from the mold by means of the ram. Since the plaster expands considerably during setting, enormous forces occur during the setting and the discharge, which must be resisted by the mold.

Since the plates manufactured by this method must satisfy rigid requirements as to accuracy of size and to surface finish, the walls of the molding boxes must be absolutely parallel and have a completely smooth surface. Hence, the production of machines of this kind requires perfect workmanship and this is reflected in the 7 high cost price of such machines.

If the box walls are exclusively chromium-plated as they have heretofore been fabricated, unfavorable phenomena may occur which puts the machine out of action. This is the case, if the chromium deposit is scratched even slightly on one wall. Since the working in such molding plants is rather rough, this may easily happen. The sulfur which is always present in plaster corrodes the supporting plate within a short time and causes corrosion pits which grow rapidly below the chromium surface. The chromium surface breaks away in scales and a hole forms in the supporting plate. Thereby the surface of the plaster plate which is discharged is damaged. Consequently the machine must be dismantled and the defect eliminated by expensive repairs.

This shortcoming isavoided by the fact that the box tion is used, the production of plates can be continued without restrictions even if the chromium surface is damaged. The corroding effect of the sulfur is checked by the plate of stainless steel. Moreover, slight defects of the chromium surface do neither impair the surface finish of the plates nor increase the friction caused by the discharge beyond the permissible limit. Hence, the teaching according to this invention ofiers a significant and cost-saving advantage.

An embodiment of a bordering wall according to this invention is explained in conjunction with the attached drawing; the invention is, however, not restricted to this specific embodiment.

FIG. 1 is a perspective view of a part of the wall, showing the individual layers broken away,

ice

FIG. 2 shows in perspective a detail of the edge of the wall, and

FIG. 3 shows on an enlarged scale the edge of the wall.

According to the invention the wall consists of a planar plate of iron 1 which is thick enough to satisfy the strength requirements of the wall to resist the setting plaster.

Bonded to plate 1 is a steel plate 2 of stainless steel which supports a layer 3 of chromium, produced by electroplating.

If the chromium layer 3 is damaged due to a mechanical elfect, for instance by being struck by a blow or the like, the sulfur contained in the plaster cannot corrode the solid supporting plate 1, since the plate 1 is protected by the steel plate 2 which is about 2 mm. thick. Due to its composition, this steel plate is able to resist the destructive action of the sulfur. If the chromium layer of the box wall is damaged only slightly this neither impairs the quality of the plates which are molded nor increases the frictioncaused at the time of discharge beyond a permissible limit.

In FIG. 2 a detail of the edge of the plate is represented. The steel plate 2 has a chamfered or tapered edge 4 in which the depth of the chamfer is about 0.25 mm. and the chamfer extends over a length of approximately 20 mm.

It is known that electroplating results in metallic deposits which are thicker at the edges of the plated object compared to the remaining zones. In objects requiring perfect accuracy to size, this fact has hitherto been taken 7 into account'by establishing an additional electric field along the edges of these objects in galvanic baths, this field having the function to moderate the metallic ions. However, the results of this process are not always satisfactory. According to the present invention, the chamfered edge 4, having the charnfer depth and length mentioned hereinabove, were found empirically and cornpensate for the increased thickness at the edges of the plates of the chrome layer. Thus, in spite of theaccumulated metallic deposit at the edges, a planar chromeplated surface is obtained for the wallwhich is very important in the present case.

Numerous modification and variation of the disclosed embodiment will become apparent to those skilled in the art without departing from the spirit of the invention as defined in the following claims.

What I claim is:

1. A box wall for aplaster molding machine, said wall comprising: a relatively thick iron plate providing structural strength for the wall, a steel plate on the iron plate having a charnfered edge and a chrome layer on the steel plate.

2. A box wall for a plaster molding machine, said wall comprising: a relatively thick iron plate providing structural strength for the wall, a steel plate secured to the iron plate and covering the same, said steel plate having a surface facing away from the iron plate, the wall further comprising a chrome layer on the surface of the steel plate which faces away from the iron plate, said plates defining marginal edges whereat said chrome layer has increased thickness, said steel plate having tapered edges to compensate for the increased thickness of the chrome layer to provide the chrome layer with a substantially planar surface.

3. A box wall as claimed in claim 2 wherein the tav pered edges of the steel plate are reduced in thickness prising a flat relatively thick iron plate providing struc- References Cited in the file of this patent UNITED STATES PATENTS Schwartz Oct. 16, 1928 Bofia Jan. 15, 1963 tural strength for the wall, a stainless steel plate adherently on-the iron plate and covering the same, and a chrome layer adherently on the steel plate isolated from the iron plate thereby. 5 

1. A BOX WALL FOR A PLASTER MOLDING MACHINE, SAID WALL COMPRISING: A RELATIVELY THICK IRON PLATE PROVIDING STRUCTURAL STRENGTH FOR THE WALL, A STEEL PLATE ON THE IRON PLATE HAVING A CHAMFERED EDGE AND A CHROME LAYER ON THE STEEL PLATE. 